1. The Urinary System

2. Ureters Slender tubes attaching the kidney to the bladder
Continuous with the renal pelvis
Enter the posterior aspect of the bladder
Runs behind the peritoneum
Peristalsis aids gravity in urine transport

3. Organs of the Urinary System
Figure 15.1a

4. Urinary Bladder Smooth, collapsible, muscular sac
Temporarily stores urine
Trigone—triangular region of the bladder base
Three openings
Two from the ureters
One to the urethra
In males, the prostate gland surrounds the neck of the bladder

5. Female Urinary Bladder and Urethra

6. Urinary Bladder Wall
Three layers of smooth muscle collectively called the detrusor muscle
Mucosa made of transitional epithelium
Walls are thick and folded in an empty bladder
Bladder can expand significantly without increasing internal pressure

7. Urinary Bladder Capacity
A moderately full bladder is about 5 inches long and holds about 500 mL of urine
Capable of holding twice that amount of urine

8. Position and Shape of a Distended and an Empty Urinary Bladder in an Adult Man
Figure 15.7

9. Urethra
Thin-walled tube that carries urine from the bladder to the outside of the body by peristalsis
Release of urine is controlled by two sphincters
Internal urethral sphincter
Involuntary and made of smooth muscle
External urethral sphincter
Voluntary and made of skeletal muscle

10. Female Urinary Bladder and Urethra

11. Urethra Gender Differences
Length
Females is 3–4 cm (1 inch)
Males is 20 cm (8 inches)
Location
Females—along wall of the vagina
Males—through the prostate and penis

12. Urethra Gender Differences
Function
Females—only carries urine
Males—carries urine and is a passageway for sperm cells

13. Micturition (Voiding)
Both sphincter muscles must open to allow voiding
The internal urethral sphincter is relaxed after stretching of the bladder
Pelvic splanchnic nerves initiate bladder to go into reflex contractions
Urine is forced past the internal urethra sphincter and the person feels the urge to void
The external urethral sphincter must be voluntarily relaxed to void

14. Fluid, Electrolyte, and Acid-Base Balance
Blood composition depends on three factors
Diet
Cellular metabolism
Urine output

15. Fluid, Electrolyte, and Acid-Base Balance
Kidneys have four roles in maintaining blood composition
Excretion of nitrogen-containing wastes (previously discussed)
Maintaining water balance of the blood
Maintaining electrolyte balance of the blood
Ensuring proper blood pH

16. Maintaining Water Balance
Normal amount of water in the human body
Young adult females = 50%
Young adult males = 60%
Babies = 75%
The elderly = 45%
Water is necessary for many body functions, and levels must be maintained

17. Distribution of Body Fluid
Intracellular fluid (ICF)
Fluid inside cells
About two-thirds of body fluid
Extracellular fluid (ECF)
Fluids outside cells that includes
Interstitial fluid
Blood plasma

18. Major Fluid Compartments of the Body
Figure 15.8

19. The Link Between Water and Salt
Solutes in the body include electrolytes like sodium, potassium, and calcium ions
Changes in electrolyte balance causes water to move from one compartment to another
Alters blood volume and blood pressure
Can impair the activity of cells

20. Maintaining Water Balance
Water intake must equal water output
Sources for water intake
Ingested foods and fluids
Water produced from metabolic processes
Thirst mechanism is the driving force for water intake

21. Maintaining Water Balance
Sources for water output
Vaporization out of the lungs
Lost in perspiration
Leaves the body in the feces
Urine production

22. Water Intake and Output

23. Maintaining Water Balance
Dilute urine is produced if water intake is excessive
Less urine (concentrated) is produced if large amounts of water are lost
Proper concentrations of various electrolytes must be present

24. Regulation of Water and Electrolyte Reabsorption
Osmoreceptors
Cells in the hypothalamus
React to changes in blood composition by becoming more active

25. Regulation of Water and Electrolyte Reabsorption
Regulation occurs primarily by hormones
Antidiuretic hormone (ADH)
Prevents excessive water loss in urine
Causes the kidney’s collecting ducts to reabsorb more water
Diabetes insipidus
Occurs when ADH is not released
Leads to huge outputs of dilute urine

26. Regulation of Water and Electrolyte Reabsorption
Regulation occurs primarily by hormones (continued)
Aldosterone
Regulates sodium ion content of ECF
Sodium is the electrolyte most responsible for osmotic water flows
Aldosterone promotes reabsorption of sodium ions
Remember, water follows salt!

27. Regulation of Water and Electrolyte Reabsorption
Renin-angiotension mechanism
Mediated by the juxtaglomerular (JG) apparatus of the renal tubules
When cells of the JG apparatus are stimulated by low blood pressure, the enzyme renin is released into blood
Renin produces angiotension II
Angiotension causes vasconstriction and aldosterone release
Result is increase in blood volume and blood pressure

28. Maintaining Acid-Base Balance in Blood
Blood pH must remain between 7.35 and 7.45 to maintain homeostasis
Alkalosis—pH above 7.45
Acidosis—pH below 7.35
Physiological acidosis—pH between 7.35 and 7.0
Most ions originate as by-products of cellular metabolism

29. Maintaining Acid-Base Balance in Blood
Acids produced by the body
Phosphoric acid, lactic acid, fatty acids
Carbon dioxide forms carbonic acid
Ammonia
Most acid-base balance is maintained by the kidneys
Other acid-base controlling systems
Blood buffers
Respiration

30. Blood Buffers Acids are proton (H+) donors
Strong acids dissociate completely and liberate all of their H+ in water
Weak acids, such as carbonic acid, dissociate only partially
Bases are proton (H+) acceptors
Strong bases dissociate easily in water and tie up H+
Weak bases, such as bicarbonate ion and ammonia, are slower to accept H+

31. Dissociation of Strong and Weak Acids
Figure 15.12

32. Blood Buffers
Molecules react to prevent dramatic changes in hydrogen ion (H+) concentrations
Bind to H+ when pH drops
Release H+ when pH rises
Three major chemical buffer systems
Bicarbonate buffer system
Phosphate buffer system
Protein buffer system

33. The Bicarbonate Buffer System
Mixture of carbonic acid (H2CO3) and sodium bicarbonate (NaHCO3)
Carbonic acid is a weak acid that does not dissociate much in neutral or acid solutions
Bicarbonate ions (HCO3–) react with strong acids to change them to weak acids
HCl + NaHCO3  H2CO3 + NaCl
strong acid weak base weak acid salt

34. The Bicarbonate Buffer System
Carbonic acid dissociates in the presence of a strong base to form a weak base and water
NaOH + H2CO3  NaHCO3 + H2O
strong base weak acid weak base water

35. Respiratory System Controls of Acid-Base Balance
Carbon dioxide in the blood is converted to bicarbonate ion and transported in the plasma
Increases in hydrogen ion concentration produces more carbonic acid
Excess hydrogen ion can be blown off with the release of carbon dioxide from the lungs
Respiratory rate can rise and fall depending on changing blood pH

36. Renal Mechanisms of Acid-Base Balance
Excrete bicarbonate ions if needed
Conserve (reabsorb) or generate new bicarbonate ions if needed

37. Renal Mechanisms of Acid-Base Balance
When blood pH rises
Bicarbonate ions are excreted
Hydrogen ions are retained by kidney tubules
When blood pH falls
Bicarbonate ions are reabsorbed
Hydrogen ions are secreted
Urine pH varies from 4.5 to 8.0

38. Developmental Aspects of the Urinary System
Functional kidneys are developed by the third month
Urinary system of a newborn
Bladder is small
Urine cannot be concentrated for first 2 months
Void 5 to 40 times per day

39. Developmental Aspects of the Urinary System
Control of the voluntary urethral sphincter does not start until age 18 months
Complete nighttime control may not occur until the child is 4 years old
Urinary infections are the only common problems before old age
Escherichia coli (E. coli), a type of bacteria, accounts for 80% of UTI (urinary tract infections)

40. Aging and the Urinary System
There is a progressive decline in urinary function
The bladder shrinks and loses bladder tone with aging

41. Aging and the Urinary System
Associated problems with aging
Urgency—feeling that it is necessary to void
Frequency—frequent voiding of small amounts of urine
Nocturia—need to get up during the night to urinate
Incontinence—loss of control
Urinary retention—common in males, often the result of hypertrophy of the prostate gland